Ammonia for use in manufacture of GaN-type compound semiconductor and method for manufacturing GaN-type compound semiconductor

ABSTRACT

Ammonia for use in the manufacture of a GaN-type compound semiconductor, filled in a charging container  18  such that at least a part of the ammonia is liquid and the liquid phase ammonia has a water concentration determined by a Fourier-transform infrared spectroscopy (FT-IR) of 0.5 vol ppm or less, is introduced in the gaseous state into a reaction chamber  11  housing therein a substrate  1 , and a layer comprising a GaN-type compound started from this ammonia is formed on the substrate  1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C. §119(e)(i) of the filing date ofProvisional Application No. 60/114,376 filed Dec. 30, 1998 pursuant to35 U.S.C. §111(b).

FIELD OF THE INVENTION

The present invention relates to ammonia for use in the manufacture of aGaN-type compound semiconductor and a method for producing a GaN-typecompound semiconductor using the ammonia.

BACKGROUND OF THE INVENTION

FIG. 3 shows an example of conventional GaN-type compound semiconductordevices. The GaN-type compound semiconductor device shown here has aconstitution such that a buffer layer 2 comprising Ga_(x)Al_(1-x)N(wherein 0≦x≦1) which is a GaN-type compound, a Si-doped n-typeGa_(x)Al_(1-x)N layer (n-type clad layer) 3 which is an n-type cladlayer doped with Si, a Zn-doped Ga_(x)Al_(1-x)N layer (active layer) 4which is a light emitting active layer doped with Zn, and a Mg-dopedp-type Ga_(x)Al_(1-x)N layer (p-type clad layer) 5 which is a p-typeclad layer doped with Mg are laminated in sequence on a sapphiresubstrate 1 and electrodes 6 and 7 are provided on the n-type clad layer3 and p-type clad layer 5, respectively.

This GaN-type compound semiconductor device can be used as a blue lightemitting diode.

FIGS. 1 and 2 show an example of a production apparatus for use in themanufacture of the above-described GaN-type compound semiconductordevice.

The production apparatus shown here is a metal-organic chemical vapordeposition (MOCVD) reactor and comprises a reaction chamber 11 forhousing a sapphire substrate, a support part 12 for holding the sapphiresubstrate in the reaction chamber 11, a heater 13 for heating thesapphire substrate supported by the support part 12, organic metalcontainers 14 and 15 as supply sources of organic metals, organic metalgas inlet tubes 16 and 17 for introducing organic metal gases suppliedfrom the containers 14 and 15 into the reaction chamber 11, an ammoniacharging container 18 as a supply source of ammonia gas, an ammonia gasinlet tube 19 for introducing the ammonia gas supplied from the chargingcontainer 18 into the reaction chamber 11, an outlet tube 20 fordischarging gases out of the reaction chamber 11, a Si compoundcontainer 23, a Zn compound container 24, a Mg compound container 25,and inlet tubes 26, 27 and 28 for introducing the compounds suppliedfrom the containers 23, 24 and 25 into the reaction chamber 11.

The epitaxial wafer for use in the manufacture of the GaN-type compoundsemiconductor device is manufactured using the above-describedproduction apparatus according to the MOCVD process as described below.

In the production of the GaN-type compound semiconductor device, asapphire substrate 1 is housed in a reactor 11, an organic galliumcompound housed in a container 14 and an organic aluminum compoundhoused in a container 15 are bubbled with H₂ gas using tubes 21 and 22,the organic gallium compound gas and organic aluminum compound gasobtained are introduced together with H₂ gas into the reaction chamber11 through inlet tubes 16 and 17, at the same time, ammonia gas suppliedfrom a charging container 18 is introduced into the reaction chamber 11through an inlet tube 19, and then a buffer layer 2 comprisingGa_(x)Al_(1-x)N is formed on the surface of the sapphire substrate 1using these organic gallium compound gas, organic aluminum gas andammonia compound gas as raw materials.

Subsequently, a Si compound supplied from a container 23 is fed into thereaction chamber 11 through a tube 26 together with the above-describedorganic gallium compound, organic aluminum compound and ammonia gas toform an n-type clad layer 3 on the buffer layer 2.

Then, a Zn compound supplied from a container 24 is fed into thereaction chamber 11 through a tube 27 together with the above-describedorganic gallium compound, organic aluminum compound and ammonia gas toform an active layer 4 on the n-type clad layer 3.

Thereafter, a Mg compound supplied from a container 25 is fed into thereaction chamber 11 through a tube 28 together with the above-describedorganic gallium compound, organic aluminum compound and ammonia gas toform a p-type clad layer 5 on the active layer 4.

The thus-manufactured epitaxial wafer is removed from the reactionchamber 11 and electrodes 6 and 7 are provided on the n-type and p-typeclad layers 3 and 5, respectively, thereby obtaining a GaN-type compoundsemiconductor device.

The above-described conventional technique is, however, disadvantageousin that the GaN-type compound semiconductor device obtained tends not tosatisfy the light emitting property, particularly brightness.Accordingly, a technique capable of producing a GaN-type compoundsemiconductor device having excellent light emitting property withoutfailure has been demanded.

SUMMARY OF THE INVENTION

The present invention has been made under these circumstances, and anobject of the present invention is to provide a method for manufacturinga GaN-type compound semiconductor, where a GaN-type compoundsemiconductor having excellent light emitting property can bemanufactured without fail.

The present inventors have found that the water concentration in theammonia gas used as a raw material in the manufacture of GaN-typecompound semiconductors has a great effect on the light emittingproperty such as brightness of the GaN-type compound semiconductor. Thepresent invention has been accomplished based on this finding.

More specifically, the ammonia for use in the manufacture of a GaN-typecompound semiconductor of the present invention is filled in a chargingcontainer such that at least a part of the ammonia is liquid, and theliquid phase ammonia has a water concentration determined by aFourier-transform infrared spectroscopy (FT-IR) of 0.5 vol ppm or less.

Furthermore, the method for producing a GaN-type compound semiconductorof the present invention comprises introducing the above-describedammonia in the gaseous state into a reaction chamber housing therein asubstrate, and forming a layer comprising a GaN-type compound using theammonia on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic constitutional view showing a production apparatussuitably used for implementing one embodiment of the method formanufacturing a GaN-type compound semiconductor according to the presentinvention.

FIG. 2 is a schematic constitutional view showing an ammonia chargingcontainer for use in the production apparatus of FIG. 1.

FIG. 3 is a partial cross section showing an example of a GaN-typecompound semiconductor device.

FIG. 4 is a partial cross section showing an example of a GaN-typecompound semiconductor device manufactured by one embodiment of themethod for manufacturing a GaN-type compound semiconductor according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One practical embodiment of the method for producing a GaN-type compoundsemiconductor according to the present invention is described below byreferring to the case where a production apparatus shown in FIGS. 1 and2 is used and a GaN-type compound semiconductor device shown in FIG. 3is manufactured.

In the production apparatus for use in the manufacturing method of thisembodiment, the ammonia in the charging container 18 filled such that atleast a part of the ammonia is liquid and the liquid phase ammonia has awater concentration determined by a Fourier-transform infraredspectroscopy (FT-IR) of 0.5 vol ppm or less.

The liquid phase ammonia preferably has a water concentration of 0.4 volppm or less, more preferably 0.2 vol ppm or less.

If the water concentration exceeds 0.5 vol ppm, the GaN-type compoundsemiconductor using the above-described ammonia tends to have reducedlight emitting properties such as brightness.

The charging container 18 may be, for example, a cylindrical chargingcontainer shown in FIGS. 1 and 2. The inner surface of the chargingcontainer is preferably subjected to a plating or a polishing treatment.The material of the charging container 18 may be manganese steel oraluminum alloy.

In the above-described ammonia, the concentration of residual impuritiesother than water is preferably 1 vol ppm or less.

The above-described ammonia for the manufacture of a GaN-type compoundsemiconductor can be produced, for example, by a method where crudeammonia is contacted with an adsorbent such as synthetic zeolite orzirconium oxide to adsorb water in the crude ammonia to the adsorbent oris superfractionated and the ammonia after the adsorption ordistillation treatment is filled in the charging container 18.

At this time, it is preferred to prevent mixing of water to the utmostin respective processes after the adsorption or distillation treatmentuntil the ammonia is filled in the charging container 18 and previouslyclean the charging container with purified ammonia or evacuate thecharging container.

In the manufacturing method of this embodiment, the GaN-type compoundsemiconductor is produced using the above-described ammonia for themanufacture of a GaN-type compound semiconductor as follows.

A sapphire substrate 1 is housed in a reaction chamber 11 and supportedby a support part 12, the reaction chamber 11 is evacuated, and then thesapphire substrate 1 is heated using a heater 13 preferably at about400° C.

Subsequently, an organic gallium compound such as trimethyl gallium(TMGa) housed in a container 14 and an organic aluminum compound such astrimethyl aluminum (TMAl) housed in a container 15 are bubbled with H₂gas using tubes 21 and 22, and the organic gallium compound gas andorganic aluminum compound gas obtained are introduced together with H₂gas into the reaction chamber 11 through inlet tubes 16 and 17.

At the same time, ammonia gas supplied from a charging container 18 isintroduced into the reaction chamber 11 through an inlet tube 19 to forma buffer layer 2 comprising Ga_(x)Al_(1-x)N obtained from the organicgallium compound gas, organic aluminum compound gas and ammonia gas, onthe surface of the sapphire substrate 1.

Then, the temperature of the substrate 1 is elevated to about 1,150° C.and a Si compound such as a silane supplied from a container 23 is fedtogether with the organic gallium gas, organic aluminum gas and ammoniagas into the reaction chamber 11 through a tube 26 to form a n-type cladlayer 3 on the buffer layer 2.

Thereafter, a Zn compound such as dimethylzinc supplied from a container24 is fed together with the organic gallium compound, organic aluminumcompound and ammonia gas into the chamber 11 through a tube 27 to forman active layer 4 on the n-clad layer 3.

Furthermore, a Mg compound such as biscyclopentadienyl magnesiumsupplied from a container 25 is fed together with the organic galliumcompound gas, organic aluminum compound gas and ammonia gas into thereaction chamber 11 through a tube 28 to form a p-type clad layer 5 onthe active layer 4.

Subsequently, the thus-manufactured epitaxial wafer is removed from thereaction chamber 11 and electrodes 6 and 7 are provided on theabove-described n-type and p-type clad layers 3 and 5, respectively, toobtain the above-described GaN-type compound semiconductor device.

According to the manufacturing method of this embodiment, the GaN-typecompound semiconductor device obtained exhibits excellent light emittingproperty such as brightness. As a result, the production yield can beimproved.

While not desiring to be bound, the reason why the GaN-type compoundsemiconductor device obtained by this manufacturing method exhibitsexcellent light emitting property is considered as follows. By settingthe water concentration in the above-described ammonia to fall withinthe above-described range, the amount of oxygen mixed into the n-typeand p-type clad layers 3 and 5 and the active layer 4, which are formedusing the ammonia as a starting material, can be reduced and the layerseach comprising such a GaN-type compound semiconductor can be preventedfrom crystallinity deterioration.

In the embodiment described above, a method of forming n-type and p-typeclad layers 3 and 5 and an active layer 4 each mainly comprisingGa_(x)Al_(1-x)N started from the above-described ammonia is described.However, the present invention is not limited thereto and theabove-described ammonia may be used for the manufacture of a GaN-typecompound semiconductor where layers comprising a GaN-type compound suchas GaN, InGaN, InGaAlN or AlGaN, are formed on a substrate.

EXAMPLES

The present invention is described in greater detail below byspecifically referring to the Examples. Unless otherwise indicated, allparts, percents, ratios and the like are by weight.

Test Example 1

A GaN-type compound semiconductor device shown in FIG. 4 wasmanufactured as follows.

The ammonia charging container used here had a volume of 10 l and wasfilled with 5 kg of liquefied ammonia. The charging container was usedby placing it in a room temperature (24° C.) condition.

A circular sapphire substrate 1 having a diameter of 50 mm and athickness of 0.3 mm was used after the surface thereof was specularlypolished.

A single crystalline sapphire substrate 1 having a c face as the mainplane was subjected to organic cleaning and supported on a support partin a reaction chamber. Then, the pressure in the reaction chamber wasreduced to 1×10⁻³ torr or less, H₂ was introduced into the reactionchamber to return the pressure in the reaction chamber to theatmospheric pressure (760 torr), and the substrate temperature wasraised to 1,150° C. while introducing H₂ into the reaction chamber at 5slm (standard l/min.), thereby thermal-cleaning the sapphire substrate1.

After lowering the substrate temperature to 450° C., a carrier gascomprising H₂ and N₂, ammonia gas and H₂ containing trimethyl aluminum(TMAl) vapor were fed into the reaction chamber at 6 slm, 1 slm and 20sccm (standard cc/min.), respectively, over a 1.5 minute period. At thistime, the amount in mol of TMAl supplied was 3.8×10⁻⁵ mol/min.

During this process, a buffer layer 31 having a thickness of about 20 nmand comprising AlN was formed on the sapphire substrate 1.

Thereafter, the supply of TMAl was stopped, the temperature of thesapphire substrate 1 was raised to 1,100° C., and while keeping thistemperature, the above-described carrier gas, ammonia gas, disilane(Si₂H₆) diluted with H₂ to 1 vol ppm, and H₂ containing trimethylgallium (TMGa) vapor were fed into the reaction chamber at 6 slm, 2.5slm, 5 sccm and 15 sccm, respectively, over a 90 minute period. At thistime, the amount in mol of TMGa supplied was 5.8×10⁻⁵ mol/min.

During this process, a n-type GaN layer 32 having a thickness of about1.5 μm and a carrier concentration of about 3×10¹⁷/cm³ was formed.

Subsequently, the supply of TMGa was stopped, the temperature of thesapphire substrate 1 was lowered to 850° C., and while maintaining thistemperature, the carrier gas, ammonia gas, diethylzinc (DEZn) dilutedwith hydrogen to 100 vol ppm, Si₂H₆ diluted with H₂ to 1 vol ppm, H₂containing TMGa vapor, and H₂ containing trimethylindium (TMIn) vaporwere fed into the reaction chamber at 6 slm, 2.5 μm, 10 sccm, 10 sccm, 5sccm and 13 sccm, respectively, over a 15 minute period. At this time,the amounts in mol of TMGa and TMIn supplied were 1.9×10⁻⁵ mol/min and7.6×10⁻⁵ mol/min, respectively.

During this process, an InGaN active layer 33 having a thickness ofabout 100 nm and containing Si and Zn impurities was formed.

Then, while keeping the sapphire substrate 1 at the same temperature asin the formation of the InGaN active layer, the supply of TMIn wasstopped and the carrier gas, ammonia gas and H₂ containing TMGa vaporwere fed into the reaction chamber at 6 slm, 4.5 slm and 1 sccm,respectively, over a 2 minute period. At this time, the amount in mol ofTMGa supplied was 3.8×10⁻⁶ mol/min.

During this process, a GaN layer 34 having a thickness of about 3 nm wasformed.

Subsequently, the supply of TMGa was stopped, the temperature of thesapphire substrate 1 was raised to 1,150° C., and while keeping thistemperature, the carrier gas, ammonia gas, H₂ containing TMAl vapor, H₂containing TMGa vapor, and H₂ containing biscyclopentadienylmagnesium(Cp2Mg) vapor were fed into the reaction chamber at 6 slm, 3 slm, 4.3sccm, 5 sccm and 135 sccm, respectively, over a 10 minute period. Atthis time, the amounts in mol of TMAl, TMGa and Cp2Mg supplied were2.3×10⁻⁶ mol/min, 1.5×10⁻⁵ mol/min and 1.1×10⁻⁴ mol/min, respectively.

During this process, a p-type AlGaN layer 35 having a thickness of about70 nm and a carrier concentration of 1×10¹⁷/cm³ was formed.

Thereafter, the supply of TMAl, TMGa and Cp2Mg was stopped, thetemperature of the sapphire substrate 1 was lowered to 1,100° C., andwhile maintaining this temperature, the carrier gas, ammonia gas, H₂containing TMGa vapor, and H₂ containing Cp2Mg vapor were fed into thereaction chamber at 6 slm, 2.5 slm, 15 sccm and 135 sccm, respectively,over a 10 minute period.

At this time, the amounts in mol of TMGa and Cp2Mg were 5.7×10⁻⁵ mol/minand 1.1×10⁻⁴ mol/min, respectively.

During this process, a p-type GaN layer 36 having a thickness of about300 nm and a carrier concentration of 3×10¹⁷/cm³ was formed.

The thus-obtained epitaxial wafer was removed from the reaction chamberand then, n-electrode 37 and p-electrode 38 were provided on the n-typeGaN layer 32 and p-type GaN layer 36, respectively, using a known deviceformation technique.

The brightness of the device obtained was measured when light wasemitted by passing a current of 20 mA in the forward direction betweenthe n-electrode 37 and the p-electrode 38 of the device. The resultsobtained are shown in Table 1.

Also, the water concentration of the liquid phase ammonia in thecharging container (at the initiation of test) is shown in Table 1below.

Test Examples 2 to 7

GaN-type compound semiconductor devices were manufactured in the samemanner as in Test Example 1 except that the water concentration ofammonia (at the initiation of test) used by filling it in a chargingcontainer was changed as shown in Table 1 below.

The light emission brightness of the thus-obtained GaN-type compoundsemiconductor devices were measured and the results are shown togetherin Table 1.

The water concentration of the liquid phase ammonia was determined bysampling and vaporizing the liquid phase ammonia in the chargingcontainer and measuring the water content in the gas obtained usingFT-IR (MAGNA560, manufactured by NICOLET).

The water concentration of the liquid phase ammonia shown here is watercontent in terms of volume percent of part per million (vol ppm) in thegas obtained by sampling and vaporizing the liquid phase ammonia.

TABLE 1 Water Concentration in Brightness Liquid Phase (vol ppm) (cd)Test Example 1 1.0 0.1 Test Example 2 0.8 0.5 Test Example 3 0.5 1.5Test Example 4 0.4 2.1 Test Example 5 0.2 2.6 Test Example 6 0.1 2.8Test Example 7 0.01 3.0

It is seen from the results in Table 1 that devices manufactured by themethod of using ammonia in which the liquid phase ammonia has a waterconcentration of 0.5 vol ppm or less, have excellent light emittingproperties.

In particular, devices manufactured by the method of using ammonia inwhich the above-described water concentration is 0.4 vol ppm or lessexhibit high brightness of 2 cd or more. Furthermore, devicesmanufactured using ammonia in which the above-described waterconcentration is 0.2 vol ppm or less have still more excellent lightemitting properties.

As described in the foregoing, according to the present invention, aGaN-type compound semiconductor having excellent light emittingproperties such as brightness can be obtained without fail and theproduction yield can be improved.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A method for manufacturing a GaN-type compoundsemiconductor light emitting device, comprising introducing ammonia inthe gaseous state into a reaction chamber housing therein a substrate,and forming a layer comprising a GaN-type compound started from theammonia on the substrate, wherein said ammonia is taken out in thegaseous state from a charging container, in a room temperaturecondition, a portion of ammonia in the charging container being in aliquid phase and another portion of ammonia in the charging containerbeing in the gas phase, and a water concentration of said liquid phaseammonia in the charging container being controlled in the range between0.01 and 0.5 vol ppm as determined by Fourier-transform infraredspectroscopy (FT-IF).
 2. A method for manufacturing a GaN-type compoundsemiconductor light emitting device according to claim 1, wherein awater concentration of said liquid phase ammonia in the chargingcontainer is controlled in the range between 0.01 and 0.4 vol ppm asdetermined by Fourier-transform infrared spectroscopy (FT-IR).
 3. Amethod for manufacturing a GaN-type compound semiconductor lightemitting device according to claim 1, wherein a water concentration ofsaid liquid phase ammonia in the charging container is controlled in therange between 0.01 and 0.2 vol ppm determined by Fourier-transforminfrared spectroscopy (FT-IR).